In certain processes, such as manufacturing processes, it is necessary to evaluate work product in order to assure that it meets specifications or otherwise falls within predetermined criteria. For example, in extrusion processes, such as tire manufacturing, rubber material is extruded and linearly drawn into a predetermined shape for use in the tire. It is important that the shape or profile of this extruded material meet predetermined design specifications. Often this determination is made via comparing a profile representing product that meets specifications with the profile of a sample of product. Several methods of evaluating such product are known and include the use of optical comparators and/or offline inspection machines. Using these machines, a cross section of product is sampled and visually compared with a reference profile by an operator to determine/assess whether or not the sample falls within the specification profile. The accuracy and reliability of this method is highly contingent upon the operator. In short, it is only as good as the operator carrying out the visual comparison.
It is also common for personnel to utilize mechanical measurement tools, such as micrometers to physically measure a product sample to assess it's compliance with specifications. Again, the accuracy of this method is highly contingent upon the operator and consistent results can not be guaranteed.
With respect to work product that is nominally round in shape, devices known as shadow gauges, such as the LaserMike™ laser micrometer by Beta LaserMike, Inc., are often employed to check the diameter of work product. These devices do not however, allow for determining anything more than cross sectional dimensions in a predetermined reference plane. Further, as the work product may move within a given work zone, the dimension measured by the shadow gauge may not be the dimension of interest at a given time due to the movement of the work product.
In order to determine if the extruded product meets specification, it is common for production to be stopped at predetermined intervals to allow a sample of the extruded rubber product to be obtained for evaluation/comparison. This means production time is lost during the process of obtaining a sample. Further, since samples are taken typically at predetermined intervals, if product begins to fall out of specification between samples intervals, product output is lost before corrective action can be taken to bring the production back into spec. This results in lost time and wasted production.
In an effort to work around the short-comings of the known inspection/evaluation methods, off-line inspection systems have been adapted to on-line processes. There are known systems that utilize, for example, motorized positioning devices to transport one and/or position one or more measuring instruments within a predetermined region of interest. The region of interest will to typically be adjacent to or surrounding an area or path along which work product is passed during a manufacturing process. These systems do not, however, provide information about all points of interest at the same point in time. If the product moves during measurement, then the data does not accurately represent the product. Another drawback to this method is the initial cost and maintenance cost for such a motorized mechanism.
More recently, machine-vision approaches have been utilized to assess the shape and profile of in-process work-product. “Smart camera” sensors from companies such as DVT, Inc. or Cognex, Inc. and structured light sources from companies such as Lasiris, Inc. can be combined to form a rudimentary measurement system. These systems suffer from inaccuracies due to non-linearity in the optics associated with the structured light sources and/or imperfections in the alignment of components that comprise the structured light source. Further, these systems do not provide the ability to inspect (evaluate) the entire profile of a work piece.
Other systems may have been introduced which incorporate an array of pre-calibrated contour sensors to allow for in-process inspection/evaluation of the complete shape and/or profile of a work piece during the manufacturing process. As each sensor in these systems must be registered (correlated) to a common coordinate space in order to allow collected data to be properly represented in relation to data collected by other sensors in the system and the work piece itself, efforts must be made to establish a correlation between the various coordinate spaces associated with each of the sensor devices and the work piece. The process for establishing a correlation between various the coordinate spaces associated with each sensor and a common coordinate space has been time consuming and cumbersome.
Further, these systems do not allow for the comparison of a work piece profile (as represented by captured profile data) with a predetermined reference profile, independent of the orientation of the work piece profile at the time of inspection/evaluation. These systems also present challenges in minimizing the areas of a work piece profile that are at least partially obscured from detection by one or more of the sensors.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.